I am using QGIS 2.18.21. The attribute table of my shapefile has 88 features but after creating the Voronoi, only 86 are in the attribute table and all the points are showing inside the Voronoi diagram.
Please, what could be wrong?
PolyGeo suggested that my comment should be turned into an answer:
There were several bugs in the QGIS Voronoi code. Many were fixed in QGIS 3.2.2 (not backported to QGIS 2.18). According to a comment from user118372 on Aug 28, upgrading to 3.2.2 solved the experienced problems.